A go-to guide for experimenting with bright colors and bold makeup.

Four short years ago, while touring with One Direction following their win on The X Factor, British glam guru (and the 1D boys’s hairstylist) Lou Teasdale received an unexpected phone call from Louis Tomlinson’s mom. The reason for her call: to ask if Louis’s younger sister, Lottie Tomlinson, could assist Lou for the remainder of the tour.

What Lou originally thought would be a “babysitting job” (she was immediately proven wrong) turned out to be the beginning of an epic best-friendship that has since given way to a stream of incredibly cool beauty tutorials conceptualized by the dynamic duo.

Lottie, who constantly wows us with her makeup and hair hacks (for instance, she's filmed one of the most impressive eyebrows tutorials we've ever seen), has spent the past few years building up her beauty resume. She put Bleach London’s intricately woven hair tapestries on the world’s radar, launched a successful collaboration with Nails Inc., and has even perfected faces backstage at London Fashion Week. Her dreamy, kaleidoscopic Instagram feed has amassed over 3.2 million followers who constantly look to her for hair and makeup inspiration, whether it’s tips for mixing metallics with burnt orange eyeshadow, or ways to rock glitter roots.

Next up, Lottie’s taking her beauty expertise to bookshelves — the 19-year-old is set to release her debut book, “Rainbow Roots,” a playful, yet comprehensive guide to makeup experimentation with every color of the rainbow (plus neon, sequins, glitter, and lip gloss) this October. To celebrate the launch, we spoke with Lottie about her brand new book, the one trend she’d never try, and her ultimate beauty muse (hint: it’s major!).

Teen Vogue: When did you first discover makeup?

Lottie Tomlinson: I remember looking through my mom’s makeup bag when I was about 12 years old, trying to work out what each product was used for. I asked her, "What does this one do?" Then I started researching all of the different products on the internet. My mom watched me do this for months and finally, one day, said I could order one product. I picked Benefit Cosmetics Erase Paste Concealer. I was so excited for it to arrive!

TV: What was the best part of putting together your new book?

LT: Coming up with all of the different looks! I was really able to express my style in these pages. It was so fun!

LT: I love experimenting with color and bright makeup. Then again, I also love using neutrals! For me, the most important thing is stepping out of your comfort zone with makeup — it’s a way to try new things. You’ll often be surprised how certain products look [after they’re applied]. It’s great a way to find your look.

TV: What facial feature do you like to play up most?

LT: Probably my eyes, but I never stick to one look with my eye makeup. There are so many things you can do with eye makeup!

LT: Filling in someone's eyebrows instantly frames their face. It’s such an important part of any makeup look.

TV: Who’s your favorite face to paint, and why?

LT: I used to love doing my mom’s make up. She had the most gorgeous face — she used to sit perfectly still with her eyes closed and a smile on her face. She always loved the end result, but maybe she was a bit biased! I'll never forget doing her makeup for her wedding day. It was such an honor.

TV: What does “beauty” mean to you? What makes someone beautiful?

LT:Everyone is beautiful. Makeup is about accentuating your beauty.

TV: Have you ever faced any major challenges that almost got in the way of your dream

LT: Confidence [has been the biggest challenge]. Beauty can be a really intimidating industry to work in. I’ve doubted myself. I’ve told myself I wasn’t good enough. Even now, I sometimes think, "These brands really want to work with me?" You just have to believe in yourself.

TV: How has social media helped to shape your career?

LT: It’s played a huge role in shaping my career — without social media, I wouldn't be doing what I’m doing today. [Instagram] is such an amazing platform to promote and share your work. It’s a place where people can come together and bond over their love for makeup.

TV: What is the most inspiring feedback you’ve gotten from your fans?

LT: Probably to be myself! They've always accepted me for who I am, and that’s given me the confidence to express myself and be more comfortable with my style.

TV: You’ve rocked some amazing hairstyles, from rainbow roots to intricate hair tapestries. What do you like most about experimenting with your hair?

LT: It's just another way of expressing yourself. It's really exciting to try something new and take a risk! I was so nervous to dye my hair green, but it turned out to be my favorite look ever.

TV: Is there any beauty trend you would NEVER try?

LT: I’ve seen the braided eyebrow trend popping up a lot on Instagram lately and I'm not really into it! Plus, it's so hard to actually achieve!

LT: I’m really loving a highlight at the moment — it's a really big trend right now. I apply highlighter to my cheekbones, down my nose, on my brow bone, and in the inner corners. It really pulls your entire look together.

TV: Is there anyone in the industry that you consider particularly inspirational?

LT: One of my biggest inspirations is Huda Kattan. She built an empire with Huda Beauty. Now, she's the biggest beauty influencer on the internet!

TV: What’s the most important lesson Lou Teasdale has taught you?

LT: Lou is my best friend. She’s taught me so much and has played a massive role in helping me get to where I am. She always pushes me to not give up and be more confident, which is really helpful for me.

TV: You have some major accomplishments in the beauty sphere. Do you have a dream project you’re hoping to work on in the future?

LT: I’d love to start my own brand one day, but I think I’ve got plenty of time to do that. I'm enjoying myself and learning a lot in the meantime!

You can get your hands on Lottie’s “Rainbow Roots,” published by Laurence King, exclusively at Topshop September 30th. It will also be available for purchase at Barnes & Noble, Amazon.com, and Nordstrom October 2nd.